Added two new signals to GtkSpinButton, "input" and "output", to make the

Added two new signals to GtkSpinButton, "input" and "output", to make the

* gtk/gtkspinbutton.[c,h] gtk/testgtk.c: Added two new signals to
	GtkSpinButton, "input" and "output", to make the output more flexible.
 	The user has to provide a mapping between adjustment->value and the
 	output string (and vice versa, if the spin button is editable).
	See testgtk for examples.